In the mouse olfactory system, 10 million olfactory sensory neurons (OSNs) extend from the epithelium into the olfactory bulb. Within the bulb, they will target and synapse with just one of ~1800 glomerular targets. This targeting of OSNs to glomeruli represents an intriguing model system in which to study pathfinding and target recognition. What are the molecular mechanisms used by OSNs to identify their appropriate glomerulus in the bulb? In this application to the Bioengineering Research Grant program, a multidisciplinary, collaborative effort that spans neurobiology and physics is proposed that will employ new techniques to identify guidance and targeting cues used by OSNs. We hypothesize that OSNs which target different glomeruli must express different guidance cues that enable them to distinguish among various targets. To identify these cues, we have focused on developing highly sensitive molecular tools. First, we have developed a technique capable of amplifying small amounts of RNA. Second, we have developed a novel microarray printing method that greatly improves the sensitivity of the microarray technique. The combination of a highly sensitive amplification technique coupled with a dramatic improvement in microarray data acquisition will provide us with a powerful screen to identify guidance cues in the olfactory system. In this application, we will further characterize and refine the fabrication of these polymer-based arrays. We will compare them against conventional arrays, and then use them to search for axon guidance cues expressed by OSNs.